Soldering has been conventionally performed for mounting an electronic component upon a printed circuit board, or electrically connecting an internal element or the like of the electronic component that is mounted upon the printed circuit board. A typically utilized solder is an eutectic solder of tin and lead, and when actually mounting an electronic component upon the printed circuit board, soldering is performed at a maximum temperature of 260° C. using a tin-lead eutectic solder with a melting point of 183° C.
Soldering for electrically connecting an electrode and an element or the like included in an electronic component that is mounted upon the printed circuit board requires maintaining a stable connection, even at the above-mentioned temperature for performing soldering on a mounting board. Consequently, a high temperature solder with a melting point of at least 260° C. must be used for internally soldering the electronic component so that the joints do not come off even under such conditions. Furthermore, a high temperature solder with little characteristic changes under high temperatures is also in demand.
Solder material of 90 wt % lead and 10 wt % tin with a solid phase temperature of 268° C. and a liquid phase temperature of 301° C., or solder material of 90.5 wt % lead, 8 wt % tin and 1.5 wt % silver with a solid phase temperature of 277° C. and a liquid phase temperature of 290° C., or the like is typically used as the high temperature solder, where these solders raise the melting point by using large quantities of lead.
Incidentally, from the viewpoint of technical simplicity, reliability and the like, soldering is essential in the manufacture and assembly of electronic devices. On the other hand, since the solder includes lead, which is harmful to the human body, the health effects for the workers at the fabricating site of the solder itself, and at manufacturing sites that utilize that solder for soldering devices or the like cannot be overlooked. At the same time, in the light of current conditions where a great deal of electrical devices that are no longer in use are disposed, environmental problems arising due to the lead-containing solder utilized for such waste products are feared.
Consequently, recycling waste products and manufacturing methods not using harmful substances are proposed. Removal of harmful substances is desired from the viewpoint of preventing environmental pollution, where joining techniques using solder is not an exception. Materialization of a high temperature solder not containing lead, which is a harmful substance, is in demand by the electronic device industry and the like.
Various techniques relating to solder not containing lead, namely lead-free have been previously proposed. For example, techniques relating to solder that is preferable for joining fittings and inner wires of control cables for brakes, clutches and the like of automobiles and motorcycles by adding tin, zinc, and silver are mentioned in Laid-open Japanese Patent Application No. 55-65341. Furthermore, techniques heightening joint strength by further adding copper are mentioned in Laid-open Japanese Patent Application No. 56-69341.
In Laid-open Japanese Patent Application No. 11-172352, techniques are mentioned where with zinc as the main material, aluminum, magnesium and gallium are added. Laid-open Japanese Patent Application No.11-172363 discloses techniques where with zinc as the main material, aluminum and germanium are added, and tin and/or indium are also added. Furthermore, solder having a composition of zinc, a material with higher vapor pressure than that of zinc, and tin is mentioned in Laid-open Japanese Patent Application No. 2000-15478.
Incidentally, copper material is typically used as material configuring electronic devices and electronic components, however when using solder containing zinc for soldering such copper material, there are cases where an intermetallic compound generates at the joint interface of the solder and the copper material if it is left under high temperatures, thereby increasing the electrical resistance.
Since this intermetallic compound is one generated from copper diffusing in the metal components of the solder and has a hard, fragile and rough structure, reduction of soldering joint strength and reduction of electrical conduction occur. These type of problems cannot be resolved with the solder composition disclosed in each of the gazettes described above.
The present invention is one that is devised with the problems described above taken into consideration, and the objective thereof is a solder that is preferable for use in electronic devices and electronic components. In particular, it aims to provide a solder not containing lead with zinc as a dominant element, and a joint not containing lead, which have stable electrical characteristics that are given by controlling the growth of intermetallic compounds at the junctions with the copper.